Safety connection for electric mains.



M. H O CHSTADTER.

SAFETY CONNECTION FOR ELECTRIC MAINS.

I APPLICATION FILED IULY25, I911.

Patented Sept. 21, 1915.

HIIIIIIIII COLUMBIA PLANDGRAPH c0., WASHINGTON. D. c.

M. HUCHSTADTER.

SAFETY CONNECTION FOR ELECTRIC MAINS.

APPLICATION FILED 1uLY25. 1911.

1,154,894. Patented Sept. 21, 1915.

5 2 $HEETSSHEET 2.

COLUMBIA PLANOGRAPH C0. WASHINGTON, D. c.

To all whom itmay concern i a subject of the German Emperor, and.re-

i LUNITEDSTATESJPATENT CE ARTIN HocHsTAn'rEn; or BERLIiLG ERNIANY,ASSIGNQR To sIEMEns-soHUo'KEnr- -WERKE e. M. B. OF'BERLIN, GERMANY, Aoonr'ona'rron or GERMANY;

Be itkno" n that I, MARTiNIICflSiTiiDTER,

siding at Berlin, Germany,- haveinvented certain new and usefulImproyements in Safety Connections forElectric Mains, of

l which the following is a. specification.

. My inventio-nrelates'to a safety' conne tion for electric mains, and,a primary object is .to' automatically disconnect from the system onlythe injured portion of the main when its; insulation ismechanicallyor'elec trically broken down. a

The arrangement according to my invention substantially consists in theaddition to each mainaaside, from the usual metallic protectivecoverings or armoring, -of a special auxiliary conductor in thehform" ofan'electrically conducting layer located in the -insulation proper, thepotential of which layer is. varied by the current due to the leakageand which causes the automatic disconnection of the defective length ofmain. The electrically conducting layer does not appreciably diminishthe flexibility of the cable. ;Moreover,.it is so disposed that it isencountered with certainty bythe are which is produced. between the mainconductor and the outer metallic armor whenever the -insulationi ispuncturedand it is thus electrically connected with the armor.

Accordingly, it is preferably made as a thin metallic layer surroundingthe vconductor concentrically with the latters longitudinal axis: Inorder to conveniently connect circuit breakersor othersuitable-apparatus 1n clrcuit w th the aforement oned conductng .layers,I connect nduction coils .or S1II11- lar suitable devices for operatingthecircuit breakers, *with the conductive layers of the mains atfthepoints where they emerge from their prctectingcoverings. Now if,v forexample, in a single cable line an'aux iliary conductor is connectedwith the ground ,at such a point by a grounded conductor or attached tothe one pole of asource of current whose other pole is grounded, theabove-mentioned arc can beusedfor start ing the disconnecting operation.The are may for instance render ineffective a closed circuit currentbyshort-circuiting it, or it may close a superposed open circuit currentby bridging over .a break provided for the purpose, th c arra gement ineach instancein Spccification of Letters'Patent.

SAFETY Conn-newton FOR ELEo'rRIc MAINs.

accordance with the character of the discon-i' necting. devices; In bothinstances the ad Patented Sept. 21, 1915. Application filed J' 1115725,1911. Serial No. 640,476.

vantage is obtained that the start'of the disconnecting operation is independent of accident, because whenever a puncture is made an arc isformed generally between the main conductor and the outer covering andsimultaneously between the auxiliary conductor and the. outer covering,aInd also because'the current due to the leakage is employed only as theelectrical connection for closing or short-circuitingthe workingcircuit, but not for operating the disconnecting vmeansitself.Consequently, in the present arrange ment no attempt is made to controlthe amount of current due to the leakager This would also serve nopurpose, because'the beginning of the disconnecting operationisindependent of .the kindand extent of the destruction of the cable atthe defective portion; of course the disconnecting relays-will operatethe more readilyand' rapidly the betterv the arcis which is formed bythe a I leakage current between the electrically con: ducting layer andthefouter metallic covering. VVhen the electrically conducting layersare skilfully arranged they must become fused with theouter-metallic.covering of theone or more cables when thelatter arepunctured] Obviously, these principal features of the invention admit ofgreat freedom in selecting the disco-nnectingdevice and in constructingthe remainder of the disconnecting circuit. I

Several illustrative embodiments of the invention are represented in theaccompanying drawings, whereinz i Figures 1 and 2. are diagrams. showingtwo arrangements of connections for closed circuit'currents, Figs. 3 and4 are diagrams showing two arrangements of connections for open circuitcurrents, and Fig. 5 is a diagram explained hereinafter. Fig. 6 is adiagram similar .to that shown iirFig. 3 illustrating. the use of anauxiliary alternating current source... e

In each illustrative embodiment is shown a branching point leading ofithe main and b twe n two of such points a cable sectiO is confined ofwhich any desired number may be thought of as connected in series or inparallel inlthe'system. ,Fig. 5, indicates a closed ring main-havingfive of such branchingpoints indicatedby the numerals and the individualvalues of th-eamount of' energy consumed. In all the five illustrativeembodiments it is assumed that three phase current is supplied. In thediagrams according to Figs. 1 and 3 the three-phase main consists ofthree single unarmored lead-covered cables and in those according toFigs. 2 and of a twisted triple cable armored with iron ribbon. Thedescribed arrangements can also be employed for alternating current ofany desired number of phases, and the arrangement according to Figs. 3and at can be used for direct current. The cable lines which I usediffer from ordinary cables owing to the good electricallyconductingmetallic layers which are embedded. according to my invention, in theinsulation of the individual conductors and separated by a: layer ofinsulation in each case from the lead covering, and in twisted cablesfrom both the lead covering and the metallic layers of the otherconductors. In single cables (Fig. 1), each conductor proper b b bsupplying energy carries a layer of insulation 71,, 71,, t',, then themetallic layer h 72. 7a,, then a second, in general thin layer ofinsulation 8,, s s and lastly the lead covering 0,, c 0,. In multiplecables, the individual conductors after being provided, as described,with a layer of insulation, then the metallic layer and a second layerof insulation, are twisted in the usual manner, provided with a commonlayer of insulation and then with a common lead covering 0 which may bewound with additional coverings, iron ribbon and jute. In thearrangement according to Figs. 1 and 2, each of theelectrically-conducting layers 7a,, 7a,, ii, of the six ends of thecables to be connected is connected by way of a choking coil CZ, to d,respectively to a common ground ed wire (1.. The choking coils, may, however, be dispensed with if desired when the layers It, to it, themselvesproduce a su'tlicient choking action, that is to say the choking coilsand the layers may thus be combined with each other. The purpose ofthese choking coils is to prevent the current due to the fault fromflowing through the tripping coils, operating the circuit breakers. Inthe diagrams according to Figs. 1 and 2 when the cable line is free fromleakage the current flowing in the coils e, to 6 as will be explainedlater, holds a member for start ing the out out operation. in itsinoperative position. Such a member may be a switch which, whenreleased, closes an auxiliary electric circuit and thereby causes asecondary cut out relay to operate the section switch. This arrangementis shown here, as is indicated by the switches f, to 7),. These switchesshown as controlled by the coils 6 may, however, if preferred beconnected with a purely mechanical device for opening the sectionswitches; consequently, in this connection the auxiliary source ofcurrent 0 does not constitute an essential part of the arrangement. Inthe present case, where a battery is arranged as shown in Figs. 1 and2*, it is in circuit with two elect'romagnets t t each magnet formingits own circuit with the battery over contacts 10, and w respectively,when the latter are closed. In this case armatures "0,, c, are attractedand thereby release switch bars 1 (1 v so that the latter are drawnupward under the action of springs p 72 and thereby opentheir respectiveswitches G This operation takes place when relays e,e,, or e,e,, aredenergized so that they drop their armatures f as previously described.

The connections represented in Figs. 1 and 2' are particularlycharacterized by the feature that the potential difference between theelectrically-conducting layers owing to their being insulated from theground, which difference I shall hereinafter terin capacity tension, isused here for producing the normal energizing current for relays e,-e,,.They are therefore suitable for only alternating currentsystems. In suchsystems a static charge is produced in the auxiliary conductor byinfluence action, the amount of which is determined by the thickness ofthe layers of insulation between the main conductor and theelectrically-conducting layer on the one hand, and between the layer andthe lead covering on the other hand. These charges become equalized byway of the choking coils (Z -cl, and the coils c ,c to the ground andthus produce the constantly flowing current requisite in the coils e,c,,for attracting the switches f .f,. Now if the cah'l-e is -unctured andleaks to ground, the capacity tensions, and when the star connectioncenter in the central station is grounded, the principal tensions, areequalized along the more convenient path to the ground by way of the areformed by the leakage current and the good electrically conducting outercovering 0. In this manner the grounded conductors are short-circuitedby way of the choking coils d and the coils eat the two ends of thedefective cable, the appertaining switches f are released and cause thenearest section switch to be opened. In the arrangements according toFigs. 3' and fl, a special auxiliary source of current 0 is provided asan essential constituent. As compared with the arrangement accord ing toFigs. 1 and 2 this has the advantage 7 that the connections can beemployed for every kind of current, including direct current. Inaddition,fo'wing to this arrangement the cut out is limited withabsolute certainty to the two ends ofthe faulty section. The specialfeature of the connections according'to Figs. 3 and 4. is that theelectrically-conducting layers h of all cable ends and their chokingcoilscl are connected behind the choking coils in star connection, and,owingto the neutral point-therebyproduced only one single connectingconductor Z and two out out relays m and n are requisite for any desiredfrequency to connect the electrically conducting: layers of all thephases; The one pole of the auxiliary source of current '0 is connectedbetween the two relaysv and its other pole may be connected by way ofwire a to the ground. The protective coverings of the cables 0 to 0 inFig. 3 and 0 in Fig. 4 are likewise grounded.

In the arrangements according to Figs. 3 or 4: when the cable leaks toground, the

are produced closes the circuit of the auxiliary source of currentbetween the conducting layer and the ground. The cut out relays m and .nare thereby energized and the section switches opened. When the cable isfree from faults a capacity tension ofcourse exists in the layers 72;when this connection is used in alternating current systems; thistension isequalized however by way of the choking coils connected'instar connection, without passing to the cut out relays or to theauxiliary source of current. As the auxiliary current in theseconnections must flow by way of the choking coils d, the auxiliarysource of current preferably supplies only direct current,'oralternating current of a lowfrequency which is considerably less thanthefrequency of the main system. Such arrangement with an alternatingcurrent source of low frequency is shown in Fig. 6 which is otherwisesimilar to Fig. 8. Instead of the direct current source 0 in Fig. 3 alow' frequency alternating current source for instance dynamo 0' isconnected in circuit.

In the above only the most important defects in practice, those from themain conductor to ground, have been mentioned. In

multiple cables, however, leakages'may oc- Such a ground 9 is proof thestation transformer. Assuming the existence of such a common point, inthe arran'gements according to Figs. 8 and 4:, the

circuit of the auxiliary source of current will then be connected incase of leakage be ground wire a and the auxiliary source of current 0to a cut out coil m or n, by way of I ground, so that the coils 6 canobtain no more current'and' must allow the switches f to fall. omitted.For when short circuit occursbetween conductor and conductor thecapacity current is cutoff from the coils e owing to the path from theelectrically conducting layers byway of the arc and the main conductorsinto the system being easier than the path byway of the choking coils ofthe auxiliary conductor.

In contradistinction to known arrange- The grounding might here be'tween two individual mains by way of, the

ments, in the safety connections according to the invention specialsignal, measuring or like conductors are expressly avoided because suchauxiliary conductors require special supervlsion and considerablylncrease the possibility of unforeseen and uncontrollable faults anddisturbances. On the other hand, the closed auxiliary circuit providedaccording to the invention comprising the electrically-conducting layersconnected in series, choking coils and cut out coils can be themselvesused for such purposes if necessary. -For instance by means of staticvoltmeters nterposed between each auxiliary layer and the ground thecondition of the insulation of'the individual sections of the cable lineand, in the case of polyphase cables, the insulation of the variousphases can be constantly checked. Thus the layers may be used for atwofold purpose, an advantage IlOtBXlStlIlg in any known safetyconnections. The above described arrange ment, has, however, thedisadvantage that in high tension systems only high tension apparatus'can be connected to the auxiliary layers. In order to obviate thisdefect and to render the auxiliary layer accessible at any time, atleast in alternating current systems, without the provision for lowtension apparatus,-according to the invention not ordinary choking coilsare employed as the necessary choking members, but small transformers,e. g; measuring transformers, to which any'deslred low tenslon apparatusand 'iron armor or the like.

measuring instruments can be connected. In this manner the auxiliarylayer can be employed in all. cases for any other desired purposes.Lastly, the present invention can also be used for protecting cablesfrom purely mechanical injury of the common metallic outer coverings, e.9. lead sheaths, To this end, each cable is provided in its activeinsulation maerial below the common outer covering with an electricallyconducting layer H of the type mentioned above which, like the outercovering, surrounds all the individual conductors in common, and, inaddition, is connected with cut out apparatus, if necessary even withchoking coils, like the electrically conducting layers surrounding theindividual conductors. In consequence of this arrangement, when injuriesoccur through picks, spades and other tools, which frequently happens inbuilding roads, foundations and the like, the electrically conductingimplement or tool meets with the are at the place where the cable ispunctured and thus forms the bridge requisite for the dis connectionbetween the electrically conducting layer and the metallic outercovering. The desired protection from mechanical in jury is obtainedmoreperfectly the nearer the electrical1yconducting layer is placed tothe outer electrically-conducting protective covering. It is preferableto diminish the distance between the electrically conducting layer andthe protective covering as much as is possible in view of themanufacture of the cable and the safety of the same when laying it, forthe nearer the electrically conducting layer is to the outer coveril'lg,the more readily will insignificant injuries of the outer coveringoperate the cut out device. Also, injuries owing to electricallynon-conducting tools and even severe bulges and sharp bends in the outerprotective covering will break through the insulating layer between theelectrically-conducting layer and. the outer covering and bring aboutthe disconnection. Simultaneously, together with the reduction of thethickness of insulation between the electrically-conducting layer andthe outer covering the tension permanently at the choking coil isdiminished and consequently the choking coil is diminished in size,become," less expensive to make and can be more readly insulated.

In systems comprising multiple cables, when employing oneelectrically-conducting layer with safety apparatus connected thereto,the electrically-conducting layers about the individual conductors, maybe omitted according to the present invention. In this event theauxiliary layer for the safety connection is formed by the electricallyconducting layer under the outer metallic protective coverings of thecables. This simplification is admissible when it is remembered that theelectrically conducting layer provided according to the invention andsurrounding all. the individual conductors sufiices in every case forbringing about the disconnection when a short circuit takes placebetween one energy conductor and the outer conducting coverings. Theconducting layers around the individual conductors are requisite solelyin case of leakages between two conductors of energy within the cablewithout the insulation of the conductors of energy against ground beingbroken down. But as a leakage between two conductors scarcely everoccurs in practice, as mentioned above, without destroying theinsulation between the conductors of energy and the ground, in thearrangement of one common electrically conducting layer arranged in themanner last mentioned, the conducting layers around the individualconductors may be safely omitted.

I claim 1 1. In an electric supply system, the combination, with a cableline and section switches interpolated therein, of an electricallyconducting layer in the insulation of each main conductor in the cableline, and grounded disconnecting means operatively connected with eachsection switch and electrically connected with the one or moreelectrically conducting layers for automatically opening the sectionswitches at the ends of a cable section in which a fault occurs.

2. In an alternating current supply system, the combination, with acable line, and section switches interpolated therein, of grounded,electromagnetically controlled, disconnecting means for opening each ofthe said section switches, and an electrically conducting layer in theinsulation of each main conductor of the cable line connected with saiddisconnecting means, the current due to the potential difference betweenthe one or more layers and the ground normally preventing saiddisconnecting means operatmg.

3. In an electric supply system, the combination, with a cable line andsection switches interpolated therein, of disconnecting means comprisinga grounded auxiliary source ofcurrent for opening each section switch,and an electrically conducting layer in the insulation of each maincondi'lctor of the cable line connected with said disconnecting means.

a. In an electric supply system, the combination, with a cable line andsection switches interpolated therein, of disconnect ing meanscomprising a grounded auxiliary source of current for opening eachsection switch, an electrically conducting layer in the insulation ofeach main conductor of the cable line connected with said disconnectingmeans, and a choking device interpolated and the appertainingdisconnecting means.

5. In a permanently grounded electric Supply system, the combination,with a cable line comprising a plurality of individual cables having acommon grounding conductor, and a plurality of sets of section switchesinterpolated in the line, of disconnecting means comprising a groundedauxiliary source of current for opening each section switch, andan'electrically conducting layer in the insulation of each individualcable of the cable line connected with said disconnecting means.

6. In a polyphase alternating current supply system, the combination,with a cable 4 line, and section switches interpolated therein, ofgrounded, electromagnetically controlled, disconnecting means foropening each of the said section switches, and an electricallyconducting layer in the insulation of each main conductor of the cableline connected in star connection with said disconnecting means, thecurrent due to the potential diflerence between the one or more layersand the ground normally preventing said disconnecting means operating.

7 In apolyphase alternating current supply system, the combination,with. a cable line, and section switches interpolated therein, ofgrounded, electromagnetically controlled, disconnecting means comprisingonly one disconnecting coil for opening each of the said sectionswitches, and an electrically conducting layer in the insulation of eachmain conductor of. the cable line connected in starconnection with saiddisconnecting means, the current due to the po- Gopies of this patentmay be obtained for tential difference between the one or more layersand the ground normally preventing 7 said disconnecting means operatlng.

8. In an alternating current supply system, the combination, with acable line, and section switches interpolated therein, of grounded,electromagnetically controlled disconnecting means comprising agroundedauxiliary source of alternating current for opening each of thesaid section switches, the frequency of the said auxiliary source ofcurrent being materially less than the main frequency, an electricallyconducting layer in the insulation of each main conductor of the cableline connected with said disconnecting means, and a choking deviceinterpolated between each electrically contacting layer and theappertaining disconnecting means. I

9. In an electric supply system, the combination, with a cable line andsection switches interpolated .therein, said cable line consisting of amultiple cable comprising a plurality of metal covered cables and acommon metallic outer covering surrounding and insulated from the same,of grounded, disconnecting means operatively connected with each sectionswitch and electrically connected with the metal coverings of the saidmetal covered cablesfor automatically opening the section switches atthe ends of a cable section in which a fault occurs.

In testimony whereof, I have signed my name to this specification in thepresence of two witnesses.

MARTIN HOCHSTADTER.

Witnesses:

WOLDEMAR HAUPT, HENRY I-IAsPER.

five cents each, by addressing the Commissioner of Patents,

Washington, D. G.

